Modified cyanoacrylate monomers and methods for preparation

ABSTRACT

Difunctional monomers of the formula, ##STR1## where R is an organic linking group derived from a diol or a dihalide of the formula X-R-X, where X is either chlorine, bromine, iodine, or hydroxy, are prepared by reacting a conjugated diene, exemplified by anthracene, with an ester of 2-cyanoacrylic acid to form the Diels-Alder adduct of the ester. The ester adduct is hydrolyzed to ultimately obtain either the Diels-Alder adduct of either 2-cyanoacrylic acid--alkali metal salt of 2-cyanoacryloyl halide. These latter intermediates are respectively reacted with either the dihalide or the diol to afford the bis-Diels-Alder adduct of the R substituted bis (2-cyanoacrylate) monomer. The protective diene group may then be removed, for example, by reaction with excess maleic anhydride and the resulting difunctional monomer isolated. 
     The difunctional monomers thus prepared can be utilized as crosslinking agents in blends comprising one or more of these difunctional monomers and at least one monofunctional monomer, exemplified by an ester of 2-cyanoacrylic acid. Alternately, one or more difunctional monomers can be homopolymerized or copolymerized to a highly crosslinked polymer. The copolymerized compositions of the monomer blends are particularly useful as adhesives, especially in dental applications for coating or sealing enamel surfaces of teeth to allay decay, or for the bonding of brackets to teeth in orthodontics the bond being substantially more resistant to moisture than where the monofunctional monomer is used alone.

This application is a CIP of my copending application Ser. No. 633,146,filed Nov. 18, 1975 which is a divisional application of Ser. No.512,276, filed Oct. 4, 1974 now U.S. Pat. No. 3,975,422 which is the CIPof applications Ser. No. 308,375 and 308,376 both filed Nov. 21, 1972and both now abandoned.

DISCLOSURE OF THE INVENTION

Field of the Invention

This invention relates to new and novel compositions and to methods forpreparing the same. In particular, this invention relates to methods forpreparing new bis esters represented by ##STR2## of the following "FlowChart" AND ##STR3## where R is an organo linking group and is a blockinggroup derived from a cyclic 1,3 diene. The monomers represented byformula I prepared by this process have been found to be particularlyuseful as adhesives, especially in dental applications when incorporatedas crosslinking agents for esters of 2-cyanoacrylic acid. The bis estersrepresented by Formula V are particularly useful in the preparation ofmonomers of Formula VI.

2. Description of the Prior Art

The production of esters of 2-cyanoacrylic acid via in situ formation ofthe Diels-Alder anthracene adducts of 2-cyanoacrylic acid esters isdescribed in U.S. Pat. No. 3,463,804. This patent, however, is concernedonly with the preparation of the monofunctional monomers, such as theesters of 2cyanoacrylic acid, and makes no reference to any means forobtaining a difunctional bis (2-cyanoacrylate) ester, such as of thisinvention, which can be polymerized alone, or in admixture with other2-cyanoacrylate esters or bis (2-cyanoacrylate) esters, to affordcrosslinked polymeric compositions. Japanese Patent 46-5135 (1971)discloses a similar process and likewise makes no reference to bis(2-cyanoacrylate) monomers.

The method disclosed in U.S. Pat. No. 3,142,698 entails the preparationof an alkylene glycol dicyanoacetate from an alkylene glycol andcyanoacetic acid. The alkylene glycol dicyanoacetate is then condensedwith formaldehyde to allegedly produce the alkylene glycol bis(2-cyanoacrylate).

Efforts to develop difunctional monomers bearing the highly reactivecyanoacrylate functional group and which can be employed as acrosslinking agent with other monofunctional monomers that polymerizethrough a vinyl bond, particularly the cyanoacrylates, have heretoforebeen without actual success.

Therefore, the primary object of this invention is to provide a methodfor preparing bis (2-cyanoacrylate) monomers and to provide compoundsthat can readily be converted to bis (2-cyanoacrylate) monomers so thatthe same can be employed as crosslinking agents, particularly formonofunctional esters of 2-cyanoacrylic acid.

A functional object of this invention is to provide crosslinkableadhesive compositions comprising 2-cyanoacrylate esters and difunctionalbis (2-cyanoacrylate) monomers which, upon copolymerization form acrosslinked polymer having improved resistance to moisture and improvedadhesive and cohesive bond strength over that obtainable through the useof the cyanoacrylate ester alone.

Another object of this invention is to provide compositions forperforming dental prophylaxis, for preparing dental restorations, or forbonding dental devices to teeth, such compositions having improvedadhesion to tooth structure as well as improved strength properties.

It is a still further object of this invention to provide a compositionfor use as a pit and fissure sealant that has improved adhesive andcohesive strength to enable it to better withstand the grinding forceswhich teeth undergo.

SUMMARY OF THE INVENTION

These and other objects and advantages are achieved by preparing the bis(2-cyanoacrylate) monomers of this invention in accordance with thegeneral reaction scheme set forth below. In this scheme the active vinylgroup, ##STR4## of a 2-cyanoacrylate ester (Formula I of Flow Chart) isfirst blocked by adding a blocking group, designated by through aconventional Diels-Alder reaction which blocking group is maintaineduntil the bis acrylate is formed. The blocking group is then removed,restoring the active vinyl groups of the bis 2-cyanoacrylate. This isillustrated in the following Flow Chart to which reference is now made.Referring to the following Flow Chart, an ester of 2-cyanoacrylic acidof General Formula I is reacted with a cyclic 1,3-diene to form aDiels-Alder adduct represented by General Formula (II). Typically, whereanthracene is employed as the 1,3 diene and isobutyl 2-cyanoacrylate asthe ester of Formula I, the Diels-Alder adduct of Formula II would be11-cyano-11-carboisobutoxy-9,10-dihydro-9,10-endoethanoanthracenerepresented as ##STR5##The adduct of General Formula II in which is theanthracene blocking group is then subjected to alkaline hydrolysisfollowed by acidification to form the corresponding 2-cyanoacrylic acidadduct represented by Formula III. Treatment with alkali forms thealkali metal salt represented by Formula (IV-A). Alternatively, the2-cyanoacrylic acid adduct of Formula (III) can be suitably converted tothe 2-cyanoacryloyl halide adduct represented by the Formula (IV-B).

The metal salt of the 2-cyanoacrylic acid adduct of Formula (IV-A) isthen reacted with a dihalide, X-R-X, where X is independently bromide,iodine, or chlorine in one approach or, in the other approach, the2-cyanoacryloyl halide adduct of Formula (IV-B) is reacted with a diolof the Formula, HO-R-OH. R, in each case is an organo linking groupdefined in more detail below. Either of these routes result in theformation of the bis-Diels-Alder adduct represented by Formula (V). Thisbis-Diels-Alder adduct may then be converted into its corresponding bis(2-cyanoacrylate) monomer, as represented by Formula (VI) by heating theadduct in the presence of excess maleic anhydride. In this reactionscheme, represents the cyclic 1,3-diene blocking group inserted in thefirst step of the sequence via Diels-Alder adduct formation. ##STR6##

The monomeric esters (I) of 2-cyanoacrylic acid are well known and aredescribed in U.S. Pat. No. 2,794,788. Since the ester group issubsequently hydrolyzed, the identity of the R' group of Formula I ofthe Flow Chart is immaterial. Therefore, R' can be C₁ to C₁₆ alkyl,cyclohexyl or phenyl. For convenience, isobutyl 2-cyanoacrylate is thepreferred ester, R' being isobutyl. In the above scheme, it should alsobe noted that M denotes a monovalent, divalent or trivalent ion derivedfrom a metal hydride, hydroxide, carbonate, alkoxide, or anorganometallic agent.

Although the anthracene radical is preferred, in which case would be##STR7## the 1,3-diene used to take part in the Diels-Alder adductformation may be selected from a large number of compounds with theadducted 1,3-diene radical as represented by being any of the radicals##STR8##where R₁ and R₂ are the same R₁ and R₂ may be H, an alkyl groupof 1 to 5 carbons, phenyl, Br or Cl. Where R₁ and R₂ are different, R₁is H and R₂ may be any of the group consisting of an alkyl group of 1 to5 carbons, phenyl, Br and Cl. where R₃ is H or CH₃ and ##STR9##

The organo linking group "R" appearing in the formulas of the above FlowChart may be any of the group consisting of

    -(CH.sub.2).sub.m -,

where m is an integer of from 1 to 20 inclusive; ##STR10## where n is aninteger of from 0 to 18 inclusive, and R₄ and R₅ are independentlyhydrogen or a C₁ to C₅ alkyl group, R₄ and R₅ not simultaneously beinghydrogen;

    --(CH.sub.2).sub.r --Z--(CH.sub.2).sub.s --,

where Z is --O--, --S--, --CH=CH--, --C.tbd.C--, ##STR11## and ##STR12##where r and s are independent integers of from 1 to 10 inclusive and rand s total from 2 to 20, R₆ and R₇ are independently hydrogen or astraight or branched chain C1 to C5 alkyl group. ##STR13## where x and yare integers of from 1 to 6 inclusive; ##STR14## where x and y are ashereinbefore defined;

    --CH.sub.2 -- (CF.sub.2).sub.z --CH.sub.2 --,

    where z is an integer of from 1 to 10 inclusive; and ##STR15## and wherein R' of Formula II is an alcohol moiety selected from C.sub.1 to C.sub.16 alkyl, cyclohexyl or phenyl.

One of the advantages of the process, as set forth in the above FlowChart, is that it uses conventional reactions known to skilled chemists.These reactions however, have been utilized in a new and novel sequenceto produce highly useful bis cyanoacrylate products which previouslycould not be made.

Thus, the basic Diels-Alder reaction, going from Formula I to FormulaII, is a well known type of reaction known and used by skilled chemistsas is the saponification reaction followed by acidification used ingoing from the compound of Formula II to that of Formula III. However,compounds of the General Formula III were not known prior to mypreparation and discovery thereof and form a critical step in theoverall process described.

In like manner the metal salt-halide basic reaction is well known forlinking together two acyl groups (the route through IV-A) as is theother route, that through IV-B wherein the carboxylic acid group isfirst converted to the acid halide and then esterified through reactionwith a dihydroxy compound.

DETAILED DESCRIPTION OF THE INVENTION Preparation of the Diels-AlderAdducts of 2-Cyanoacrylic Acid Esters and 2-Cyanoacrylic Acid

The difunctional monomers are prepared according to the method of thisinvention by the reaction of an ester of 2-cyanoacrylic acid (I) with a1,3-diene to form the intermediate Diels-Alder adduct (II). Thisreaction is suitably carried out in an inert solvent such as, forexample, benzene, toluene, or xylene or mixtures thereof. The reactiontemperature can be anywhere from 5° C to the reflux temperature of thesolution, depending on whether the reaction is exothermic orendothermic. The reaction is preferably carried out at the refluxtemperature in benzene as solvent or, where the reaction is exothermic,at the ambient reaction temperature or at room temperature and below.Suitable dienes include those which will undergo 1,4-cyclo-addition witha dienophile and which addition can be reversed after formation of themonomer adduct (V), such as, for example, by the application of heat orthe addition of a more reactive dienophile such as maleic anhydride.

In this regard, cyclic 1,3-dienes are much preferred over the acyclicdienes (e.g., butadiene, isoprene, 1,3-pentadiene), since they affordDiels-Alder adducts with endobridges and which are more prone towardssubsequent removal of the protective 1,3-diene moiety via aretrograde-diene scission. The bis-isoprene adduct intermediatecorresponding to adduct V, for example, is highly resistant towardsreverse Diels-Alder reaction, either thermally or by reaction withexcess maleic anhydride. Typical examples of suitable cyclic 1,3-dienesare anthracene, the 9-substituted and 9,10-disubstituted anthracenes(9-methylanthracene, 9-bromoanthracene, 9-phenylanthracene;9,10-dimethyl, -dibromo-, and -diphenylanthracenes), cyclopentadiene,methylcyclopentadiene, and norbornadiene. Preferred dienes from anavailability standpoint, ease of adduct formation and subsequentretrograde-diene scission to the difunctional monomer (VI) in goodyields and purity are anthracene, the 9-monosubstituted anthracene and9,10-disubstituted anthracenes, and cyclopentadiene.

The preferred dieneophile is isobutyl 2-cyanoacrylate, and the reactionof this latter cyanoacrylate with anthracene will yield theanthracene/isobutyl 2-cyanoacrylate adduct (II) in nearly quantitativeyield.

The 1,3-diene/alkyl 2-cyanoacrylate adduct (II) is then subjected tohydrolysis, preferably alkaline hydrolysis, to form the correspondingadduct of 2-cyanoacrylic acid (III). The hydrolysis is generally carriedout in an aqueous alcoholic solution comprising the adduct of the esterof 2-cyanoacrylic acid (II) and an alkali metal hydroxide, and thesolution is heated until the hydrolysis has been accomplished. Thereaction is complete after one to five hours at reflux, but it ispreferred to effect alkaline hydrolysis in as short a time as possible,preferably within one to two hours, to minimize or preclude concomitanthydrolysis of the cyano functional group. The hydrolyzed adduct is thenacidified with hydrochloric acid, for example, to a pH of 2 and thecrystalline Diels-Alder adduct (III) of 2-cyanoacrylic acid collected,washed with water, and dried.

Preparation of the Diels-Alder Adducts of 2-Cyanoacrylic Acid -- MetalSalts and 2-Cyanoacryloyl Halides

The 2-cyanoacrylic acid adduct (III) is then converted to either the2-cyanoacryloyl halide adduct (IV-B) or the 2-cyanoacrylic acid - metalsalt adduct (IV-A).

The 2-cyanoacrylic acid - metal salt adduct (IV-A) is suitably preparedby neutralizing an alcohol or acetone solution of the 2-cyanoacrylicacid adduct (III) with an alcoholic solution of an alkali metalhydroxide. Generally, the alcoholic solution of the alkali metalhydroxide is added dropwise to the solution of the acid adduct (III)until the pH is about 9.0, which pH has been determined to be theequivalence point. Preferred alkali metal hydroxides are sodiumhydroxide and potassium hydroxide.

Alternate methods for preparation of the alkali metal salt adducts(IV-A) include the addition of stoichiometric quantities of alkali metalhydrides, preferably sodium hydride; alkali metal alkoxides, preferablysodium methoxide, sodium ethoxide, and potassium t-butoxide; alkalimetal carbonates such as sodium carbonate and potassium carbonate; andorgano lithium compounds such as butyl lithium and the like to thesolution or suspension of the 2-cyanoacrylic acid adduct (Formula III).

The preferred metal salts of the 2-cyanoacrylic acid adduct (III) arethose of the alkali metals in Group I of the Periodic Table, preferablysodium, potassium, and lithium. Adduct-metal salts (IV-A) of certain ofthe Group II elements, exemplified by magnesium, calcium, zinc, andbarium, and trivalent metals from Group III, such as aluminum, can alsobe prepared from the requisite metal oxides, metal hydroxides, and metalcarbonates.

The 2-cyanoacryloyl halides (IV-B) are prepared by reaction of the2-cyanoacrylic acid adduct (III) with the halide reactant, preferablythionyl chloride or thionyl bromide, under anhydrous conditions in asuitable dry solvent, e.g., benzene, and in an inert atmosphere. Whileonly a samll excess of the thionyl halide reactant is required, a25-200% excess is preferably employed. Alternately, a still largerexcess of the thionyl halide can be utilized to function as both thesolvent and reactant. Reaction is enhanced by employing a very smallamount of either pyridine or N,N-dimethylformamide (DMF) asaccelerators. The reaction is effected in an inert atmosphere attemperatures ranging from 5° C to 80° C and for about 1 to 4 hours, oruntil reaction is completed, as indicated by cessation of the evolutionof hydrogen chloride and sulfur dioxide. Acid halide adduct (IV-B) isisolated by distillation in vacuo to remove any solvent and unreactedthionyl halide and purified by recrystallization from an inert solventor, if sufficiently volatile, distallation under reduced pressure. Asynthesis of the anthracene/2-cyanoacryloyl chloride adduct isexemplified in Example VI.

The 2-cyanoacryloyl halide adduct (IV-B) can also be prepared byutilizing reacants such as phosphorus trichloride and phosphoruspentachloride, whose use is well known to those skilled in the art.

After formation of either the adduct 2-cyanoacrylic acid alkali metalsalt (IV-A), or of the adduct of 2-cyanoacryloyl halide (IV-B), theserespective intermediates are employed by respective reaction with adihalide or diol to form the bis-Diels-Alder adduct of the bis(2-cyanoacrylate) monomer (V).

Preparation of the Bis-Diels Alder Adducts (V) of Bis (2-cyanoacrylate)Monomers

In general, about two moles of the Diels-Alder adduct (IV-A or IV-B) areemployed for each mole of dihalide or diol reactant. Suitable dihalideor diol reactants include organic compounds having two reactive halogenor hydroxy substituents thereon, the dihalide of which will undergo adisplacement reaction with the carboxylate salt and the diols of whichundergoes an acrylation reaction with the 2-cyanoacryloyl halide to formthe bis Diels-Alder adducts (V) of the bis (2-cyanoacrylate) monomers.Examples of such compounds, wherein X is either independently selectedfrom the halogens chlorine, bromine, iodine, or from hydroxy, include:

A. X--(CH₂)_(m) --X, where m is an integer of from 1 to 20 inclusive,such as methylene iodide, 1,3-dibromopropane, 1,9-dibromononane,1,12-dibromododecane, 1,3-propanediol, 1,9-nonanediol, and1,12-dodecanediol.

B. ##STR16## where n is an integer of from 0 to 18 and R₄ and R₅ areindependently selected from the group consisting of hydrogen and C₁ andC₅ alkyl, but R₄ and R₅ not simultaneously being hydrogen; such as1,3-dibromobutane, 2,5-dibromohexane, 1,3-butanediol, and2,5-hexanediol.

C. X--(CH₂)_(r) --Z--(CH₂)_(s) --X, where Z is --O--, --S--, --CH=CH--,--C.tbd.C--, ##STR17## where r and s are independent integers of from 1to 10 inclusive and r and s total from 2 to 20, R₆ and R₇ being asheretofore defined. The substitution on the aromtic ring is meta, para,or ortho; meta or para being preferred. The hydrogen atoms of the vinylsubstituent are either cis or trans. Examples include: 2-chloroethylether, diethylene glycol, 4-chlorobutyl ether, 4-hydroxybutyl ether,2-chloroethyl sulfide, 2-hydroxyethyl sulfide, 3-chloropropyl sulfide,3-hydroxypropyl sulfide, trans-1,4-dibromo-2-butene,trans-2-butene-1,4-diol, trans-1,8-dichloro-4-octene,trans-4-octene-1,8-diol, trans-1,12-dichloro-6-dodecene,trans-6-dodecene-1,12-diol, 1,4-dichloro-2-butyne, 2-butyne-1,4-diol,1,8-dichloro-4-octyne, 4-octyne-1,8-diol, 1,12-dichloro-6-dodecyne,6-dodecyne-1,12-diol, 1,3-dibromo-2,2-dimethylpropane,1,3-dihydroxy-2,2-dimethylpropane, 4,4'-bis (chloromethyl) diphenylether, 4,4'-bis (hydroxymethyl) diphenyl ether and neopentyl glycol.

D. Alkylene glycols of the formula

HO[R"O]_(t) H, where when t is ≧ 1, R" is propylene, and when t is>2, R"is also 1,4-tetramethylene and ethylene. The polyalkylene glycols aresuitable in the higher molecular weight ranges generally to about amolecular weight of about 2000. Examples include propylene glycol,dipropylene glycol, polypropylene glycol, triethylene glycol,tetraethylene glycol, polyethylene glycol, and poly (1,4-tetramethyleneglycol).

E. ##STR18## where the susbstitution on the aromatic ring is meta, para,or ortho, and x and y are integers of from 1 to 6 inclusive such as1,4-bis(chloromethyl) benzene, 1,4-bis(hydroxymethyl) benzene,1,4-bis(4-bromobutyl) benzene, 1,4-bis(4-hydroxybutyl) benzene,1-chloromethyl-4-(4-chlorobutyl) benzene and1-hydroxymethyl-1-4-(4-hydroxybutyl) benzene.

F. ##STR19## where x and y are as hereinbefore defined and thesubstitution on the ccyclohexane ring is 1,2; 1,3; or 1,4 such as1,4-bis (chloromethyl)cyclohexane, 1,4-bis(hydroxymethyl)cyclohexane,1,4-bis(4-bromobutyl)cyclohexane, 1,4-bis(4-hydroxybutyl) cyclohexane,1-chloromethyl-4-(4-chlorobutyl)cyclohexane, and1-hydroxymethyl-4-(4-hydroxybutyl) cyclohexane.

G. X--CH₂ --(CF₂)_(z) --CH₂ 13 X, where z is an integer of from 1 to 10inclusive such as 1,5 -dibromo-2,2,3,3,4,4-hexafluoropentane,1,5-dihydroxy-2,2,3,3,4,4-hexafluoropentane,1,10-dibromo-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9, -hexadecafluorodecane, and1,10-dihydroxy-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecane.

H. X--CH₂ --Si(CH₃)₂ --O--Si(CH₃)₂ --CH₂ --X such as1,3-bis(chloromethyl)tetramethyldisiloxane or 1,3-bis(hydroxymethyl)tetramethyldisiloxane.

The reactants, metal salt adduct (IV-A) and dihalide, are admixed in dryN,N-dimethyl formamide (approximately 2 ml. per gram of combinedreactants) and are heated with stirring at 50 to 150° C for from 10minutes to 24 hours. The resulting solution, containing suspended alkalimetal halide solids, is then added in small increments with stirring to10 volumes of water. The precipitate of bis-anthracene adduct (V) iscollected by suction-filtration, washed thoroughly with water, andair-dried to constant weight. The adduct can suitably be furtherpurified by recrystallization from an appropriate solvent and/orchromatography on alumina, activity grade I, acid or neutral. Inchromatographic purification, bis-anthracene adducts are eluted rapidlyfrom the column with the less polar solvents, e.g., benzene,benzene-hexane, or benzene-chloroform blends. Polar impurities anddegradation products are usually selectively adsorbed and retained onthe chromatographic column.

When the bis-anthracene adduct is obtained as a gummy or oily product onaddition to water in the above procedure, it is extracted into eitherbenzene or chloroform. The extract is backwashed thoroughly with water,dried over anhydrous magnesium sulfate, and solvent stripped. Residualadduct, generally a low melting solid or gum, is best purified furtherby column chromatography as described. Purification of bisanthraceneadducts is much preferred in order to obtain good yields of high puritybis (2-cyanoacrylate) monomers in the next and last step in thesynthetic sequence.

In the alternate method for bis-anthracene adduct (V) formation from the2-cyanoacryloyl halide adduct (IV-B), the latter can be prepared in situand then reacted with the diol or it can be isolated as a pureintermediate and used as such.

For example, a reaction mixture consisting of equimolar quantities ofthe anthracene/2-cyanoacrylic acid adduct (III) and thionyl chloride inbenzene (about 3 ml. per gram of total reactants) containing a smallamount of pyridine of DMF as accelerator is stirred at from 5° C to 80°C at from 1 to 4 hours or until reaction is completed (cessation ofevolution of hydrogen chloride and sulfur dioxide). To the solution ofin situ produced acid chloride adduct is added dropwise, with stirring,a solution of the stoichiometric quantity of the diol and excesstriethylamine dissolved in approximately an equal volume of DMF. Thereaction is exothermic and can be effected at the ambient temperature orpreferably, at reduced temperatures such as 5° C to 25° C. Reaction isessentially instantaneous and can be effected, depending on rate ofaddition and temperature control, within 15 minutes to 3 hours. Thereaction mixture is then diluted with additional benzene and extractedrepeatedly with water. After drying the benzene extract and solventstripping, the crude bis-antracene adduct (V) is purified by eitherrecrystallization from a suitable solvent or chromatography on alumina,activity grade I, acid or neutral, as herein before described.

The pure anthracene/2-cyanoacryloyl chloride adduct, for example, can beprepared by reaction of the 2-cyanoacrylic acid adduct (III) withstoichiometric quantities or a 25-200% excess of thionyl chloride inrefluxing benzene (about 2 to 10 ml. per gram total reactants) or otherinert solvent until reaction is completed, as idicated by completesolution of the adduct (III) and cessation of evolution of hydrogenchloride and sulfur dioxide. The solvent and excess thionyl chloride areremoved by distillation in vacuo and the crude acid chloride adductpurified by recrystallization from an inert solvent, such as benzene orbenzene-hexane blends.

The anthracene/2-cyanoacryloyl chloride adduct (IV-B) thus prepared isdissolved in dry DMF (about 1-5 ml. per gram acid halide). Withstirring, a solution of the stoichiometric quantity of the diol and anexcess of thriethylamine in one to five volumes of dry DMF is addeddropwise over 15 minutes to 3 hours and at temperatures ranging from 5°C to the ambient temperatures generated from the exothermic reaction.Bis-anthracene adduct (V) is isolated by quenching the reaction mixturein ten volumes of water. The precipitated bis-anthracene adduct (V) isfiltered, washed well with water, dried, and purified byrecrystallization from a suitable solvent or by chromatography onalumina. If the crude adduct obtained on quenching in water is a gum oroily product, it is isolated and purified by either of severalprocedures hereinbefore described.

Displacement of the Diene Protecting Group from Adduct V to YieldDifunctional Monomers

The displacement of the protecting group can be performed by heating,but in many instances the temperature required to achieve displacementof the protecting group will risk polymerization, or at leastdegradation, of the difunctional monomer. Therefore, the preferreddisplacement if effected under lower temperature conditions in thepresence of a more reactive dienophile exemplified by maleic anhydride.The bis-anthracene adduct is reacted with at least an equivalent amount,preferably with an excess, and most preferably a 50-200% excess ofmaleic anhydride. The reaction mixture is dissolved in suitable inertsolvent such as xylene or benzene, xylene being preferred. Where xyleneis used the mixture is heated with stirring at about 140° C, the refluxtemperature of the solvent. This heating is continued for 7-24 hours oruntil reaction is completed and the reaction mixture cooled to roomtemperature. The anthracene/maleic anhydride (A/MA) by-product whichcrystallizes out in high yields is collected suitably bysuction-filtration, for example, and washed thoroughly with dry SO₂-treated benzene. The filtrate is solvent stripped at about 50° C underreduced pressure to a residue, from which the xylene is removed byrepeated additions of dry benzene and solvent stripping to a residue(monomer, excess maleic anhydride, and residual A/MA adduct).

The flask containing the crude monomer is connected to a receiver flaskfitted with a condenser and a vacuum take-off adapter on top of thecondenser. The receiver flask is cooled in a solid carbon dioxide bath,and the flask containing the monomer and excess maleic anhydride heatedwith stirring at 50° to 100° C, preferably 60°-80° C (oil bathtemperature), and at 0.1-0.2mm pressure. Excess maleic anhydride readilysublimes off and is collected largely in the cooled receiver flask. Anyresidual maleic anhydride on the inside, upper walls of the flask can bedriven off with gentle heating with a jet of heated air. The flaskcontents, after cooling to room temperature, are taken up in dry, SO₂-inhibited benzene and cooled to room temperature. Additional smallamounts of A/MA adduct and polymeric by products are usually filteredoff at this stage. Concentration of the filtrate and crystallizationfrom either benzene or benzene-hexane in the cold affords thecrystalline bis (2-cyanoacrylate) monomers. Where the monomer is aliquid, as much of the residual A/MA adduct is fractionally crystallizedout as possible and the solution solvent stripped to give the liquidmonomer.

The following detailed examples will serve to provide specificillustration of the methods of preparing the difunctional monomers.

EXAMPLE I Preparation of11-Cyano-11-carboisobutoxy-9,10-dihydro-9,10-endoethanoanthracene (II)

A solution of 178.2 g (1.00 mole) anthracene (>98% purity) and 153.2g(1.00 mole) isobutyl 2-cyanoacrylate (IBC) in 1000 ml. dry, SO₂-inhibited benzene is refluxed for 17 hours. The yellow solution isconcentrated to a volume of about 600 ml. and cooled in a refrigerator.The crystalline adduct is then suction-filtered, washed with benzene andhexane, and air-dried. The yield is 224.5 g, mp. 77°-79° C. The filtrateis solvent stripped and the residue recrystallized from 350 ml. 95%ethanol to give two additional crops of product: 100.1 g, mp 92°-96° C,and 15.2 g, mp 94°-98° C. The three crops of crystals are combined andrecrystallized from 95% ethanol to give several crops of purifiedproduct: 234.5 g, mp 99°-100° C; 29.0 g, mp 98.5°-100° C; 9.5 g, mp100.5°-101.0° C. The total yield is 273 g or 82.5% of theory.

An analytical sample, recrystallized from 95% ethanol and dried over P₂O₅ at 60° C/0.4 mm, showed a mp of 100°-101° C. Anal: Calcd. for C₂₂ H₂₁NO₂ : C, 79.73%; H, 6.39%; N, 4.23%. Found: C, 79.58%; H, 6.23%; N,4.00%.

EXAMPLE II Preparation of11-Cyano-9,10-dihydro-9,10-endoethanoanthracene-11-carboxylic acid (III)

Into a 3-liter round bottom flask fitted with a mechanical stirrer,condenser, and heating mantle is charged 248 g (0.750 mole)anthracene/IBC adduct, 900 ml. 95% ethanol, and a solution of 73.3 g(1.13 moles) of potassium hydroxide (86.4%) dissolved in 375 ml. water.The deep red colored (sometimes a transient violet color) solution isstirred at reflux for 1.5 hours. The pale orange colored solution isquenched into 4000 ml. water. After standing at room temperatureovernight, the suspension (free anthracene) is filtered and the filtercake washed thoroughly with water. The clear yellow filtrate isacidified to pH 2 by the dropwise addition with stirring of 6 Nhydrochloric acid. The crystalline white solids are collected, washedwith water, and air-dried to constant weight. The yield ofanthracene/2-cyanoacrylic acid adduct, mp 201°-202° dec., is 189.0 g(91.8% theory).

Neutralization Equivalent:Calcd: 275.31 Found: 277.8.

An analytical sample, recrystallized from acetone/hexane, showed mp.208°-209° C. dec.

Anal: Calcd for C₁₈ H₁₃ NO₂ : C, 78.53%; H, 4.76%; N, 5.09%

Found: C, 78.46%; H, 4.69%; N, 5.35%

EXAMPLE III Alternate Preparation of11-Cyano-9,10-dihydro-9,10-endoethanoanthracene-11-carboxylic acid (III)

A mixture consisting of 356.6g (2.00 moles) anthracene (90+%) and 306.4g(2.00 moles) isobutyl 2-cyanoacrylate in 2000 ml. benzene is refluxedfor 4.5 hours and cooled to room temperature. No unreacted anthracenecrystallized from the solution. The latter is solvent stripped on asteam bath at water aspirator pressures to a heavy slurry of crystallinesolids. Ethanol (500 ml) is added to the solids residue and thesuspension stripped to a pasty solids residue again. This process isrepeated with another 2X 500 ml. 95% ethanol in order to srip off thebulk of the residual benzene. The residue is diluted with 2000 ml.ethanol. A solution of 195 g (3.00 moles) of potassium hydroxide (86%w)in 1000 ml. water is then added. The reaction mixture is stirred at amoderate reflux for two hours, quenched in 7000 ml. water, and theprecipitated anthracene (42.5 g, mp 212°-216° C) filtered off afterstanding at room temperature overnight. The filtrate is acidified to pH2.0 with 6N hydrochloric acid, and the precipitated adductsuction-filtered, washed thoroughly with water, and air-dried toconstant weight. The yield of anthracene/2-cyanoacrylic acid adduct is482.3g (88% theory), mp 200°-204° dec.

Adduct yields in five other runs ranged from 89 to 93%. Recovery ofanthracene is about 5-12% w of that charged.

EXAMPLE IV Preparation of Potassium11-Cyano-9,10-dihydro-9,10-endoethanoanthracene-11-carboxylate (IV-A)

Into a 5 liter three-neck round bottom flask fitted with a mechanicalstirrer, dropping funnel, and single proble pH electrode is charged asolution of 530 g (1.93 moles) of anthracene/2-cyanoacrylic acid adductin 2000 ml. absolute methanol. With stirring and dropwise addition of asolution of 20% w/v potassium hydroxide in 95% ethanol, the solution pHis adjusted from 2.0 to the equivalence point, generally 9.0-9.1 pH. Thesuspension of solids is solvent stripped in vacuo to a pasty solidsresidue. Residual alcoholic solvent is removed by dilution with 500 mlacetone and stripping to moist solids. The solids are suspended in 2500ml. acetone, stirred well at room temperature for one hour,suction-filtered, and the white solids washed thoroughly with acetone.The yield of adduct-potassium salt is 603 g (100% theory).

EXAMPLE V Anthracene/2-Cyanoacrylic Acid Adduct -- Sodium Salt (IV-A)

A solution of 19.1 g (0.0695 mole) anthracene/ 2-cyanoacrylic acidadduct in 100 ml. 95% ethanol is adjusted to the equivalence point bythe dropwise addition of 50%w aqueous sodium hydroxide solution. Heavycrystallization of solids takes place on cooling to rooom temperature.The suspension is concentrated on a rotating evaporator to white solidswhich are dried in a desiccator over Drierite for two days and then in avacuum oven at 60° C for 3 hours. The yield of adduct-sodium salt is22.2g. The infrared spectrum is consistent with the proposed structure.

EXAMPLE VI Anthracene/2-Cyanoacryloyl Chloride Adduct (IV-B)

A mixture consisting of 5.5 g (0.020 mole) anthracene/2-cyanoacrylicacid adduct, 2.9 ml. (0.040 mole) thionyl chloride, and 20 ml. drybenzene containing one drop of pyridine as accelerator is heated atreflux under nitrogen for two hours. On cooling to room temperature,heavy crystallization of the acid chloride adduct takes place. Thebenzene and excess thionyl chloride are removed on concentrating thesuspension to dryness under reduced pressure with a rotating evaporator.The crude residual product is recrystallized from 1:1 dry benzene-hexaneto give 4.7g of adduct, mp 77°-86° C, faint yellow needles.Concentration of the mother liquors gives another 0.7g adduct, mp.79°-81° C. The combined yield of 5.4g is 92% of the theoretical amount.

Infrared and NMR spectral data are consistent with the structure of theadduct. Further proof of structure is obtained on conversion of the acidchloride adduct with ethanol and ethylene glycol, respectively, to theanthracene/ethyl 2-cyanoacrylate (mp 123°-125° C) andbis-anthracene/ethylene glycol bis (2-cyanoacrylate) (mp 206°-210° C)adducts.

EXAMPLE VII Bis-Anthracene Adduct of Ethylene Glycol Bis(2-Cyanoacrylate) (V) - via Potassium Salt Adduct (IVA)

a suspension of 62.7 g (0.200 mole) anthracene/ 2-cyanoacrylic acidadduct-potassium salt and 18.8 g (0.100 mole) 1,2-dibromoethane in 150ml. of dry DMF is heated with stirring to 100° C. The adduct-potassiumsalt is solubilized within about 10 minutes followed by the depositionof finely divided potassium bromide. After 1 hour at 100° C, thereaction mixture is added dropwise with stirring to 1500 ml. of water.The suspended product is stirred for one hour, collected viasuction-filtration, washed thoroughly with water and lastly with a largevolume of 95% ethanol (to remove entrained water and ethanol solubleimpurities). The yield of bis-anthracene adduct is 48.7 g, mp 203°-206°C. A second crop of 4.4 g, mp 203.0°-206.5° C, deposited slowly from theethanolic filtrate. The total yield is 53.1 g (92% theory).

In five runs on a 0.1 to 0.8 molar scale, the yields of adduct ranged75-94% of theory.

EXAMPLE VIII Bis-Anthracene Adduct of Ethylene Glycol Bis(2-Cyanoacrylate) (V) via the Sodium Carboxylate Salt Adduct (IVA)

To a stirred solution of 13.8g (0.05 mole) anthracene/2-cyanoacrylicacid adduct in 50 ml. dry DMF is added, in portions 2.40g (0.05 mole)sodium hydride (50% in oil). Effervescence (hydrogen evolution) and amild exotherm takes place during the in situ formation of the sodiumsalt. The suspension of solids is cooled to room temperature and 4.7g(0.05 mole) 1,2-dibromoethane added. The reaction mixture is stirred atroom temperature for 17 hours with no apparent reaction (an aliquotdeposited heavy white precipitate of acid adduct on acidification). Thesuspension, on heating to 100° C, becomes homogeneous. After 3 hoursreaction at 100° C, the mixture is quenched in 400 ml. water to give13.3 g of crude bis-adduct, mp 93°-143° C. Chromatography on 136galumina, acid, activity grade I, and elution with benzene andbenzene-chloroform gives several fractions of purified adduct.Recrystallization from either benzene or acetone/hexane gives severalcrops (4.0 total, 28% theory) of the bis-anthracene adduct of ethyleneglycol bis (2-cyanoacrylate) showing mp. 204°-209°, 202°-205°,205.5°-209.0°, 209°-211.5°, and 202°-205° C,

EXAMPLE IX Bis-Anthracene Adduct of Ethylene Glycol Bis(2-Cyanoacrylate) (V) via Anthracene/2-Cyanoacryloyl Chloride AdductFormed In Situ (IVB)

Into a 250 ml. round bottom flask fitted with a stirrer, thermometer,and nitrogen inlet adapter is charged, under nitrogen, 10.0g (0.0364mole) anthracene/ 2-cyanoacrylic acid adduct, 50 ml. dry benezene, 1.0ml. DMF (as accelerator), and 4.4 ml (0.037 mole) thionyl chloride. Thesuspension is stirred at room temperature for 15 minutes and heated to50° C (complete solution took place). After 3 hours at 60° C, the orangesolution is cooled to room temperature. With stirring, a solution of1.13 g (0.0182 mole) ethylene glycol and 3.68 g (0.0364 mole)triethylamine in 5 ml. DMF is added dropwise over 15 minutes. A moderateexotherm ensues, depositing fine solids (Et₃ N.HCl). Since the resultantsuspension is still acidic, another 1.0 ml. of triethylamine was addedand the mixture stirred at room temperature for 1.25 hours. The reactionmixture is diluted with 50 ml. benzene and the solution washed fourtimes with water. The benzene extract is dried over anhydrous magnesiumsulfate, filtered, and solvent stripped to gummy yellow-orange solids(10.0g). Crystallization from acetone gives 0.7g of crude product, mp188°-210° C. Solvent stripping of the filtrate and slurrying of thegummy residue in 100 ml. of hot ethanol gives another 5.8g, mp.188°-197° C, of yellow solids. The two crops are combined (6.5g, 62%yield) and slurried in hot ethanol (300 ml) to give 4.1 g (39% theory)or purified product, mp 192°-201° C. Recrystallization fromchloroform/ethanol gives 2.9g showing mp 201°-203° C. Furtherpurification via chromatography on 25g alumina, acid, activity grade I,and elution with chloroform gives 1.3g of pure bis-anthracene adduct,white crystals, mp 208.5°-209.5° C.

EXAMPLE X Bis-Anthracene Adduct of Ethylene Glycol Bis (2-Cyanoacrylate)(V) via Pure Anthracene/2-Cyanoacryloyl Chloride Adduct (IVB)

Into a reaction flask fitted with an addition funnel, thermometer,drying tube, and magnetic bar stirrer is charged 5.9g (0.020 mole)anthracene/2-cyanoacryloyl chloride adduct and 5.0 ml. dry DMF. Withstirring, a solution consisting of 0.62g (0.010 mole) ethylene glycoland 3.0 g (0.030 mole) triethylamine in 5 ml. dry DMF is added dropwiseover about 30 minutes. The reaction is exothermic, and the temperatureis maintained at about 23° C with external cooling during the additionstep. The flask contents are poured into 150 ml. water, and the gummyproduct is extracted into 2×50 ml. benzene. After backwashing thecombined extracts with water, the extract is solvent stripped to give4.9g of a gum. On stirring in 100 ml. boiling 95% ethanol, the gum isconverted to white solids of the bis-anthracene adduct, 3.1g, mp206°-210° C. A mixed mp with adduct prepared via the potassiumcarboxylate adduct and 1,2-dibromoethane showed mp 205°-210° C, or nodepression.

EXAMPLE XI Ethylene Glycol Bis (2-Cyanoacrylate); (EGBCA)

A suspension of 62.7 g (0.200 mole) anthracene/2-cyanoacrylic acidadduct-potassium salt and 18.8 g (0.100 mole) 1,2-dibromoethane in 150ml. of dry DMF is heated with stirring to 100° C. The adduct-potassiumsalt is solubilized within about 10 minutes followed by the depositionof finely divided potassium bromide. After 1 hour at 100° C, thereaction mixture is added dropwise with stirring to 1500 ml. of water.The suspended product is stirred for one hour, collected viasuction-filtration, washed thoroughly with water and lastly with a largevolume of 95% ethanol (to remove entrained water and ethanol solubleimpurities). The yield of bis-anthracene adduct is 48.7 g, mp 203°-206°C. A second crop of 4.4 g, mp 203.0°-206.5° C, deposited slowly from theethanolic filtrate. The total yield is 53.1 g (92% theory).

In five runs on a 0.1 to 0.8 molar scale, the yields of adduct ranged75-94% of theory.

A mixture of 57.7g (0.100 mole) bis-anthracene/EGBCA adduct, 58.8 g(0.600 mole) maleic anhydride, 200 ml. dry xylene (SO₂ -inhibited), 0.2g hydroquinone, and 1.0 g phosphorous pendoxide is heated at 140°-145° Cfor 7 hours. The resultant suspension is cooled to room temperature andthe anthracene/maleic anhydride adduct (A/MA) is collected, washed wellwith dry benzene, and oven-dried; yield=50.7 g (92% theory), mp260°-265° C. The filtrate is solvent stripped to a liquid residue anddiluted with 3 × 100 ml. dry benzene and solvent stripped each time to aresidue. The semi-crystalline residue is taken-up in 100 ml benzene, letstand at room temperature one hour, and filtered to give an additional6.6 g, mp 248°-256° C, of A/MA adduct. The filtrate is solvent stripped,and the excess maleic anhydride is sublimed off at 70° C (0.2mm).Dilution of the crystalline residue with 75 ml. dry benzene gave another1.7 g, mp 246°-258° C, of A/MA. The total recovery of A/MA adduct is59.0 g (107% theory).

The filtrate is solvent stripped and the residue slurried in 50 mlbenzene, cooled in an ice bath one hour, suction-filtered, and the whitecrystals washed with benzene to give 8.7 g, mp 103°-105° C, of ethyleneglycol bis (2-cyanoacrylate) monomer (EGBCA).

The following additional crops of EGBCA were isolated after solventstripping of the mother liquors, sublimation of small additional amountsof maleic anhydride, and crystallization from benzene: 3.1 g, mp99°-103° C; 3.0 g, mp 100°-104° C; 0.3 g, mp 98°-103° C. The total yieldof EGBCA is 15.1g (69% theory).

An analytical sample, recrystallized twice from benzene, showed mp104°-105° C.

Anal: Calcd for C₁₀ H₈ N₂ O₄ : C, 54.55%; H, 3.66%; N, 12.72%.

Found: C, 54.75%; H, 3.69%; N, 12.61%.

The IR and NMR spectra were consistent with the proposed structure. Themonomer was soluble in practically all common organic solvents, e.g.,acetone, chloroform, dioxane, ethyl acetate and aromatic hydrocarbons(warm), but not in the aliphatic hydrocarbons.

EXAMPLE XII 1,3-Propanediol Bis (2-Cyanoacrylate)

In a manner analogous to Example I, a mixture consisting of 62.7g (0.200mole) anthracene/2-cyanoacrylic acid adduct-potassium salt, 20.2 g(0.100 mole) 1,3-dibromopropane, and 165 ml dry dimethylformamide (DMF),is heated at 100° C for 1 hour and added dropwise with stirring to 1800ml. water. The white solids are collected, washed with water, andair-dried to give 51.2 g, mp 95°-106° C, of adduct. A second crop, 2.9g, mp. 91°-101° C, can be recovered from the filtrate. The total yieldis 54.1 g (91.5% theory). The NMR and IR spectra are consistent with thebis-adduct structure.

Reaction of 47.2 g (0.080 mole) bis-anthracene/1,3 propanediol bis(2-cyanoacrylate) adduct, 47.2 g (0.480 mole) maleic anhydride, 190 ml.dry xylene (SO₂), 0.1 g hydroquinone, and 0.5 g phosphorous pentoxide at140°-145° C for four hours gives 42.9 g (97% theory) of A/MA adduct,some polymeric gel, and three crops (7.1 g, 38% theory) of productmonomer showing mp 74°-78°, 75°-77° and 64°-77° C. Recrystallizationfrom dry benzene gave additional polymer (orange gum) and 6.1 g (33%theory) of pure product monomer, mp 79°-81° C.

EXAMPLE XIII 1,4-Butanediol Bis (2-Cyanoacrylate); (1,4-BDBCA)

Similarly, 15.7 g (0.05 mole) anthracene/2-cyanoacrylic acidadduct-potassium salt and 5.4g (0.025 mole) 1,4-dibromobutane in 40 ml.dry DMF are heated one hour at 100°-105° C and quenched in 400 ml. waterto yield 13.1 g, mp. 162°-172°, and 1.2 g, mp. 166°-169° C, of crudeadduct. Recrystallization from chloroform/ethanol gives 12.7 g (84%theory) of purified bis-adduct, mp 168°-175° C.

TLC (1:1 CHCl₃ /C₆ H₆): Rf 0.34 + trace amounts of impurities. All TLCprocedures described herein were conducted on Eastman 6060 Silica Gelchromatogram sheet.

Recrystallization of the 12.7 g adduct from 150 ml. benzene gives 10.9 gwhite crystals, m.p. 198°-203° C, the higher melting polymorphic form.Concentration of the mother liquors gives two of the polymorphic formsshowing mp 175°-176° C and mp 198°-206° C. It should be noted thatmixtures of two or more polymorphic forms of bis-adduct are generallyisolated. This gives rise to a number product-crops showing wide meltingpoint ranges (e.g. 164°-201° C). Heating in various solvents can oftensuffice to convert one form into another.

A mixture of 30.2 g (0.05 mole) bis-anthracene/1,4-butanediol bis(2-cyanoacrylate) adduct, 29.4 g (0.300 mole) maleic anhydride, 100 ml.dry xylene (SO₂), 0.1 g hydroquinone, and 0.5 g of phosphorous pentoxideis heated at 137°-143° C for 7 hours. Work-up according to the generalscheme gives 27.2 g (99% theory) of A/MA adduct and a total of fivecrops (7.4 g, 60% theory) of monomer, mp. 76°-79°, 76°-78°, 75°-82°,77°-79°. Recrystallization from toluene and toluene-hexane gives 4.5 g,mp 77.5°-79.0° C, and 0.7 g, mp 78.5°-80.0° C, of pure 1,4-BDBCA monomer(42% theory).

EXAMPLE XIV trans-2-Butene-1,4-Diol Bis (2-Cyanoacrylate); (t-1,4-BDBCA)

Reaction as above of 62.7g (0.200 mole) anthracene/2-cyanoacrylic acidadduct-potassium salt and 21.4 g (0.100 mole) trans-1,4-dibromo-2-butenein 160 ml. dry DMF at 100° C for 1 hour followed by addition to 1600ml.water gives 60.1 g, mp 93°-100° C. and 1.9 g, mp 93°-95° C, ofmethanol-washed adduct. Recrystallization of the combined solids frombenzene give two crops of adduct: 25.3 g, mp 104°-107° C, and 11.7g, mp145°-148° C. A third crop, 11.4 g, mp 148°-150° C, is obtained onaddition of hexane to the mother liquors. Total yield, 48.4 g (80%theory).

The first crop (25.3 g), on suspension in 250 ml boiling ethanol andfiltration, yields 19.4 g, mp. 178°-179° C., of the higher meltingpolymorphic form. Combination of the second and third crops (23.1g) andslurrying in hot ethanol gives another 20.8 g, mp. 149°-152° C, of thelower melting polymorph. Further work-up of various mother liquors gives2.3 g white crystals (from benzene) showing mp 101.5°-108° C. All threepolymorphic forms of the bis-adduct showed Rf 0.5 on TLC in 1:1 CHCl₃/C₆ H₆.

A mixture consisting of 36.2 g (0.06 mole)bis-anthracene/trans-2-butene-1,4-diol bis (2-cyanoacrylate) adduct,35.3 g (0.36 mole) maleic anhydride, 120 ml. dry xylene (SO₂), 0.12 ghydroquinone, and 0.6 g phosphorous pentoxide is stirred at gentlereflux for 7 hours and cooled to room temperature. The crystalline A/MAadduct is collected, washed with dry benzene, and dried in vacuo; yield= 30.3 g (92% theory), mp 256°-257° C. The filtrate is solvent strippedto a liquid residue which is redissolved in several portions of drybenzene and solvent stripped to a residue each time. The residue, oncrystallization from 50 ml. benzene in an ice bath, gives 6.4 g of crudemonomer, mp 108°-120° C. The crude monomer is slurried in 50 ml. boilingbenzene and filtered hot from the two crops of insoluble A/MA adduct(2.6 g, mp 257°-260° C and 0.4g, mp. 255°-260° C). The benzene solubles,on concentration and crystallization from benzene/hexane, afford 2.0 g,mp 106°-108°, and 0.6 g, mp 105°-108° C of additional monomer.

The mother liquor from the 6.4 g monomer fraction is solvent strippedand additional maleic anhydride sublimed off at 80° C (0.1 mm).Crystallization of the residue from 25 ml. benzene gives 6.3 g, mp.104°-105° C (162° clear melt), and 2.9 g, mp. 103°-104° C, of monomer.The total yield of t-1,4-BDBCA monomer is 11.8 g (80% theory).

Recrystallization from benzene of combined monomer (19.1g) from two runsgives some polymeric solids and 12.8 g of pure t-1,4-BDBCA, mp 105°-107°C, white needles. Concentration of the mother liquors gives twoadditional crops; 0.9 g, mp 100°-105° C, and 1.3 g, mp 93°-105° C.

The total yield of A/MA adduct recovered is 33.3g (100% theory).

EXAMPLE XV 2,5-Hexanediol Bis (2-Cyanoacrylate); (2,5-HDBCA)

A mixture of 62.7g (0.200 mole) of anthracene/2-cyanoacrylic acidadduct-K salt, 24.4 g (0.100 mole) 2,5-dibromohexane, and 150 ml of dryDMF are heated at 100° C for one hour and added dropwise to 1500 mlwater. The white solids are collected, washed with water, and air-dried.The yield of bis-adduct, mp 84°-86° C, is 60.0 g (94.8% theory).

Bis-adduct from another run showed mp. 87°-92° C; TLC (1:1 CHCl₃ /C₆H₆): Rf 0.6.

A mixture consisting of 56.0 g (0.0885 mole) bisanthracene/2,5-HDBCAadduct, 52.0g (0.531 mole) maleic anhydride, 0.1 g hydroquinone, and 1.0g phosphorous pentoxide in 220 ml. dry, SO₂ inhibited xylene is heatedat 138°-142° C for 8 hours, cooled to room temperature, and filtered togive 31.7 g, mp 264°-268° C, of the A/MA adduct. After solvent strippingto remove residual xylene, the excess maleic anhydride is sublimed offat 65°-80° C/0.2 min. The orange gummy residue is crystallized frombenzene in the cold to give another 5.5 g, mp 261°-267° C, of A/MAadduct. Concentration of the filtrte and crystallization frombenzene/hexane gives 0.8 g of white solids showing mp 73°-190° C.Further concentration and cooling give additional white solids. Thelatter are collected, washed successively with benzene, 1:1benzene/hexane, and hexane to give 1.6 g of product monomer, mp 80.0° -80.5° C.

EXAMPLE XVI 1,3-Bis(Hydroxymethyl) Benzene Bis (2-Cyanoacrylate)

A mixture consisting of 15.6 g (0.050 mole) anthracene 2-cyanoacrylicacid adduct-K salt and 4.3 g (0.025 mole) 1,3-bis (chloromethyl) benzenein 40 ml. dry DMF is heated at 100° C for 1 hour and added dropwise,with stirring, to 500 ml. water. The fine solids are collected bygravity filtration, washed with water and methanol, and air-dried togive 10.5 g pale yellow solids, mp 105°-110° C. Two additional crops,0.2 g, mp 113°-118° C, and 2.3 g, mp 98°-104° C, are obtained byconcentration of the methanolic washes. The total yield is 13.0 g (82%theory). TLC (1:1 CHCl₃ /C₆ H₆): Rf 0.6 (bis-adduct) + Rf 0.9(anthracene) + traces of polar impurities (for all three crops).

In another run on a 0.05 mole scale, the yield of crude bis-adduct, mp.86°-88° C, was 30.9 g (98% theory), white solids.

A mixture consisting of 30.0 g (0.0474 mole) bisanthraceneadduct/1,3-bis (hydroxymethyl) benzene bits (2-cyanoacrylate), 27.8 g(0.284 mole) maleic anhydride, 0.1 g hydroquinone, and 0.5 g phosphorouspentoxide in 125 ml. dry xylene is heated at 139°-141° C for 5 hours,cooled to room temperature, and suction-filled to give 26.1 g, mp257°-259° C, of A/MA adduct. Solvent stripping of the filtrate andcrystallization of the residue from benzene gives another 3.5 g, mp258°-260° C, of A/MA adduct. The mother liquor is solvent stripped andthe excess maleic anhydride sublimed off at 60°-65° C/0.1-0.2mm. Thesemi-crystalline residue (11.4g) is taken-up in 50 ml. hot benzene, thesolution decanted from some insolubles (3.5 g, mp>300° C) and cooled togive another 1.3 g, mp 260°-262° C, of A/MA adduct. The filtrate isconcentrated in vacuo to give 6.2 g (44% theory) of crude monomer as apale orange liquid. IR and NMR analysis indicated the presence ofconsiderable anhydride-containing and other unknown impurities.

EXAMLE XVII 1,3-Bis(hydroxymethyl)tetramethyldisiloxane Bis(2-Cyanoacrylate)

A mixture consisting of 125.4 g (0.400 mole) anthracene/2-cyanoacrylicacid adduct-K salt and 46.2 g (0.200 mole) 1,3-bis (chloromethy)tetramethyldisiloxane in 340 ml. dry DMF is heated at 100° C for 1 hourand quenched in 3400 ml water. The gummy product is twice extracted into500 ml portions of benzene, and the combined extracts are washed with4×250 ml water, 1×250 ml saturated sodium chloride solution, and thendried over magnesium sulfate. The dried solution is concentrated toabout 400 ml and filtered slowly through a column of 500 g. alumina,neutral, activity I, at a fast dropwise rate and eluted further with anadditional 1000 ml benzene. Solvent stripping gives 98.9g (70% theory)of the bis-adduct as a colorless gum.

The NMR and IR spectra are consistent with the proposed structure. Someextraneous peaks due to impurities are seen in the NMR scan but not inthe IR spectrum.

In another run using 1,3-bis (bromoethyl) tetramethyldisiloxane asreactant, the purity of the crude bis-adduct isolated via benzeneextraction is very similar to that obtained from the dichloro reactant.Chromatography on alumina, acid, activity I, affords a 64% recovery ofbis-adduct on elution with 1:1 benzene-hexane, benzene, 1:1benzene-chloroform and chloroform. Only a marginal improvement in purityis obtained for some fractions, and there is strong indication ofproduct degradation on the column.

A mixture consisting of 52.7 g (0.0743 mole) bisanthraceneadduct/1,3-bis (hydroxymethyl) tetramethyldisiloxane bis(2-cyanoacrylate), 43.8 g (0.446 mole) maleic anhydride, 0.1 ghydroquinone, and 1.0 g phosphorous pentoxide in 190 ml. dry, SO₂-inhibited xylene is heated at a gentle reflux (140° C) for 8 hours,cooled to room temperature, and filtered to give 30.6 g, mp 258°-262° C,of A/MA adduct. The filtrate is solvent stripped to a dark orange syrupwhich is taken-up in 50 ml. benzene and filtered to give an additional4.2 g, mp. 258°-261° C, of A/MA adduct. The resultant filtrate isconcentrated to a syrupy residue again and the excess maleic anhydrideis sublimed off at 65°-75° C/0.2mm. The pot contents are slurried in 25ml. benzene and filtered to afford 1.0 g, mp 235°-258° C, of A/MAadduct. The mother liquors are concentrated to about 50 ml. and dilutedwith about 25 ml. hexane to give, in two stages, an additional 0.3 g.and 0.2 g. of A/MA adduct. A final solvent stripping of the filtrategives 22.3 g (85% theory) of the bis (2-cyanoacrylate) monomer, abrown-orange syrupy liquid. The total A/MA adduct yield is 36.3 g (89%theory).

IR and NMR assay confirmed the identity of the monomer but indicatedcontamination by some residual A/MA adduct and other unknownsilicone-containing impurities.

EXAMPLE XVII

In a manner analogous to the above examples, the following difunctionalmonomers are also prepared:

methylene glycol bis (2-cyanoacrylate) from methylene iodide;

1,3-butanediol bis (2-cyanoacrylate) from 1,3-dichlorobutane;

1,5-pentanediol bis (2-cyanoacrylate) from 1,5-dichloropentane;

1,6-hexanediol bis (2-cyanoacrylate) from 1,6-dichlorohexane;

1,6-hexanediol bis (2-cyanoacrylate) from 1,6-dibromohexane;

1,7-heptanediol bis (2-cyanoacrylate) from 1,7-dibromoheptane;

1,8-octanediol bis (2-cyanoacrylate) from 1,8-dibromooctane;

1,9-nonanediol bis (2-cyanoacrylate) from 1,9-dichlorononane;

1,10-decanediol bis (2-cyanoacrylate) from 1,10-dibromodecane;

1,12-dodecanediol bis (2-cyanoacrylate) from 1,12-dichlorododecane;

1,12-dodecanediol bis (2-cyanoacrylate) from 1,12-dibromododecane,

2-butyne-1,4-diol bis (2-cyanoacrylate) from 2-butyne-1,4 diol;

neopentyl glycol bis (2-cyanoacrylate) from neopentyl glycol;

1,4-bis (hydroxymethyl) benzene bis (2-cyanoacrylate) from 1,4-bis(chloromethyl) benzene; and

Bis(4-hydroxybutyl) ether bis (2-cyanoacrylate) from bis(4-hydroxybutyl) ether.

EXAMPLE XVIII Cyclopentadiene/IBC Adduct (Isobutyl2-Cyano-5-Norbornene-2-Carboxylate) (II)

To first prepare the cyclopentadiene monomer, dicyclopentadiene (95%,Enjay Chemical) is charged into a round bottom flask fitted with amagnetic bar stirrer, 30 cm, Vigreux column packed with Berl saddles,and a distillation head/receiver. The dimer is heated with stirring,under nitrogen and at atmospheric pressure, to reflux. After collectinga small forerun cut at bp 28°-36° C, the cyclopentadiene monomer iscollected at bp 36°-40° C in a Dry Ice cooled receiver. The monomer isused immediately in the following step.

Into a one-liter round bottom flask fitted with a thermometer,condenser, Drierite drying tube, dropping funnel, nitrogen inletadapter, and a magnetic bar stirrer is charged 92.2g (1.40 moles)cylopentadiene monomer (freshly distilled), 500 ml dry benzene, and 0.1gp-methoxyphenol. The solution is cooled with stirring to 5° C and tothis added, over 1 hour and at 5-15° C, 214g (1.40 moles) isobutyl2-cyanoacrylate (inhibited with excess SO₂). The exotherm subsidesquickly after the addition of isobutyl 2-cyanoacrylate. The ice bath isremoved and the solution stirred at room temperature overnight. Thesolution is solvent stripped to give 312.6g (102% theory) of crudeadduct, a colorless liquid. The latter is inhibited with 0.1gp-methoxyphenol and distilled in vacuo through a 6 inch Vigreux column.Pure isobutyl 2-cyano-5-norbornene-2-carboxylate is collected at bp 91°C (0.4mm) - 96° C (0.6mm). The yield of colorless distillate is 287.0g(94% theory). TLC: 1:1 C₆ H₆ /CHCl₃, Rf 0.7; C₆ H₆, Rf 0.84 (all TLCprocedures were conducted on Eastman 6060 Silica Gel chromatogramsheets). On the basis of NMR, there is approximately a 60/40 ratio ofthe two expected stereoisomers.

EXAMPLE XIX Cyclopentadiene/2-Cyanoacrylic Acid Adduct(2-Cyano-5-Norbornene-2-Carboxylic Acid) (III)

To a solution of 250 g (1.14 moles) isobutyl2-cyano-5-norbornene-2-carboxylate (IBC/CPD adduct) in 1000 ml. 95%ethanol is added a solution of 112 g (1.71 moles) of potassium hydroxide(86%w) in 1000 ml. water. The solution is refluxed on a steam bath forone hour, diluted with 3500 ml. water, and extracted with 2 × 400 ml.benzene to remove any unreacted ester. The aqueous phase is acidified topH 1 with 6 N HCl and the oily product extracted into 4 × 200 ml.chloroform. The combined extracts are backwashed with 3 × 200 ml. water(which removed the orange color), dried over anhydrous sodium sulfate,and solvent sripped to give 182.3g (98% theory) of the crude adduct, apale orange syrupy liquid. Crystallization from benzene/hexane givesthree crops of purified 2-cyano-5-norbornene-2-carboxylic acid: (1) 89.7g, mp 87.5°-92° C, (2) 34.2 g, mp 87.5°-96.5° C, and (3 ) 15.9 g, mp.85°-90° C.

A sample, mp 88-96° C, from an earlier run showed spectralcharacteristics consistent with the proposed structure. The NMR spectrumshows that the ratio of steroisomers is now 80/20 (vs 60/40 in the esterprecursor).

Neutralization Equiv. (mp 88°-96° C): Found, 163.9Calcd, 163.2.

EXAMPLE XX Cyclopentadiene/2-Cyanoacrylic Acid Adduct - Potassium Salt(Potassium 2-Cyano-5-Norbornene-2-Carboxylate) (IV-A)

A stirred solution of 134.0 g (0.822 mole)2-cyano-5-norbornene-2-carboxylic acid in 400 ml. anhydrous methanol isadjusted from pH 1.5 to pH 9.0 (equivalence point) by the dropwiseaddition of a solution of 20% w/v potassium hydroxide in 95% ethanol.The solution is solvent stripped to a gum which is taken up severaltimes in acetone and concentrated to a gummy residue each time. The gum,on trituration with 1:1 acetone -- benzene (900 ml), gives white solids.Filtration, washing with acetone, and air-drying gives 92.5 g ofproduct, mp 188°-189° C dec. Concentration of the filtrate to 400 mlgives another 19.9 g, mp. 188° C dec. Solvent stripping to a syrupyresidue and crystallization from acetone/hexane and acetone gives twomore crops of product; 22.6 g, mp. 188.0°-188.5° C dec. and 21.2 g, mp.190°-191° C dec. The total yield of potassium2-cyano-5-norbornene-2-carboxylate is 156.2 g (94% theory).

EXAMPLE XXI Bis-Cyclopentadiene Adduct/Ethylene Glycol Bis(2-Cyanoacrylate); [Ethylene GlycolBis(2-Cyano-5-Norbornene-2-Carboxylate)]

A mixture of 40.3g (0.200 mole) potassium2-cyano-5-norbornene-2-carboxylate, 18.8g (0.100 mole)1,2-dibromoethane, and 118 ml. dry DMF is heated at 100° C for one hourand quenched in 1200 ml. water. The orange gum is extracted into 1 × 200ml. and 2 × 100 ml. chloroform, and the combined extracts are washedwith 4 × 100 ml. water, dried over a mixture of magnesium sulfate anddecolorizing carbon, filtered, and solvent stripped to an orange syrupyliquid (34.0g, 96%). The crude product is chromatographed on 200 galumina, neutral, activity I, and eluted with benzene (600 ml) to give23.9g (68% theory) of bis-adduct, a colorless syrupy liquid. The NMRspectra of the 34.0g and 23.9g fractions were essentially identical andconsistent with the proposed structure. The yield reduction is due toproduct degradation on the column.

EXAMPLE XXII Ethylene Glycol Bis (2-Cyanoacrylate) (EGBCA) viaBis-Cyclopentadiene Adduct/EGBCA (V)

A mixture consisting of 10.0g (0.0284 mole) bis-cyclopentadiene/ethyleneglycol bis (2-cyanoacrylate) adduct, 16.7g (0.170 mole) maleicanhydride, 0.1g hydroquinone, and 0.5g phosphorus pentoxide in 53 ml.dry xylene (SO₂ inhibited) is refluxed at 138°-142° C for seven hoursand cooled to room temperature. A small amount of white solids (0.8g, mp243°-245° C), probably homopolymer, is collected via suction-filtration.The filtrate is solvent stripped to a yellow syrup from which theresidual xylene is removed by periodic additions of benzene and solventstripping. The excess maleic anhydride is sublimed off at 70°-75°C/0.1mm. The residual syrup, which crystallized on cooling, was taken-upin 75 ml. hot benzene, filtered from the insoluble gelatinous polymer(0.8g), and concentrated to a yellow syrup (14.1g). The latter istriturated several times with hot hexane and benzene/hexane mixtures.The extracts give several crops of white needles on cooling to roomtemperature or below: 1.6 g. mp. 105°-122° C; 3.8g. mp. 74°-122° C;0.5g. mp 85-136° C; 0.2g. mp. 87°-136° C, 0.2g, mp. 119°-136° C. Theresidual nonextractable yellow syrup afforded 2.0g (32% theory) of EGBCAmonomer, mp 96°-103° C (mixed mp 100°-104° C), on crystallization frombenzene in the cold.

EXAMPLE XXIII Norbornadiene/Isobutyl 2-Cyanoacrylate Adduct (II);4-Carboisobutoxy-4-cyanotetracyclo[ 4.2.1.0²,9.0³,7 ] nonane.

Into a 100 ml. round botton flask fitted with a condenser, thermometer,magnetic stirring bar, and a Drierite filled drying tube is charged 18.4g (0.200 mole) norbornadiene, 30.6 g (0.200 mole) isobutyl2-cyanoacrylate (inhibited with excess sulfur dioxide), and 0.1 ghydroquinone monomethyl ether (MEHQ). The solution is stirred and heatedunder a nitrogen atmosphere to 110° C. After 15 minutes at 110° C., thesolution became cloudy, more viscous, and the reflux rate diminished.The mixture is then heated to 150° C. and maintained at this temperaturefor 24 hours. The solution is cooled to room temperature, diluted with200 ml. hexane, filtered to remove polymeric solids, and the filtratesolvent stripped to a dark orange syrupy residue. The latter isdissolved in 200 ml. acetone and to the resultant solution is added 800ml. of an aqueous solution containing 96 g. of potassium permanganateand 96 g. magnesium sulfate. After several minutes, the excess potassiumpermanganate is destroyed by bubbling sulfur dioxide gas into thesolution. The manganese dioxide precipitate is filtered and the solidswashed thoroughly with acetone. After dilution of the filtrate withone-half of its volume with water, the product is extracted intochloroform. The extract is backwashed with 3 × 500 ml. water, dried overanhydrous magnesium sulfate, filtered, and solvent stripped underreduced pressure to give 27.2 g (56% theory) of crude adduct.Distillation affords 24.0 g (49% theory) of the purenorbornadiene/isobutyl 2-cyanoacrylate adduct, b.p. 110°-112° C. (0.4mm), a colorless liquid.

EXAMPLE XXIV Norbornadiene/2-Cyanoacrylic Acid Adduct (III);4-Cyanotetracyclo[ 4.2.1.0²,9.0³,7] nonane-4-carboxylic acid.

Into a flask fitted with a condenser and magnetic stirring bar ischarged 12.3 g (0.05 mole) norbornadiene/isobutyl 2-cyanoacrylic acidadduct and a solution of 4.9 g 86% potassium hydroxide (0.075 mole) in75 ml. of water. After heating at reflux for 1.5 hours, the solution iscooled to room temperature and extracted with 2 × 25 ml. of hexane toremove any nonsaponified adduct. The aqueous phase is acidified to pH 2with 6 N hydrochloric acid and the liberated oily product is taken up in100 ml. ethyl acetate. The extract is filtered to remove some whiteinsoluble solids (0.9 g., m.p. 182° C.) and the filtrate washed with 3 ×25 ml. water, 1 × 25 ml. saturated sodium chloride solution, and solventstripped in vacuo to a pale yellow, viscous oil (8.7 g.).Crystallization of the oily product from benzene/hexane in the coldaffords 4.2 g of the norbornadiene/2-cyanoacrylic acid adduct, whitecrystals, m.p. 83°-86° C. Another 3.0 g. of adduct, m.p. 81°-84° C., isobtained on concentration of the mother liquors and cooling. Thecombined crops and adduct are recrystallized from 1:2 benzene/hexane toafford 5.9 g of pure adduct, white crystals, m.p. 81°-83 ° C.

Anal: Neutralization Equivalent: Found, 189.06 g/equiv.; Calculated(Theory), 189.22 g/equiv.

EXAMPLE XXV

In a manner analogous to that of Example XXI, the difunctional monomersspecified in Example XVII are prepared from the corresponding bis(2-cyano-5-norbornene-2 -carboxylic acid) esters of the diols.

Thus, having described the preparation of the bis esters of thisinvention, specific embodiments which utilize these bis esters will nowbe described.

In the broadest aspect, the individual difunctional bis(2-cyanoacrylate) monomers can be either homopolymerized orcopolymerized and employed as adhesives for joining or filling thevarious materials previously noted, or can be used as protectivecoatings on various materials, such as paper goods. Those difunctionalmonomers which are crystalline solids at room temperature requiredissolution in some solvent before they can advantageously be employedas an adhesive or coating material. Such a solvent may include acomonomer of this invention which is liquid at room temperature, such as1,3-bis (hydroxymethyl) tetramethyldisiloxane bis (2-cyanoacrylate);other monomers which act as a solvent for the bis (2-cyanoacrylate) andcan be copolymerized therewith; or if one or more of only the solid bis(2-cyanoacrylate) monomers are employed, a solvent such as the aromatichydrocarbons or other mutually miscible aprotic solvents. The use ofthese later solvents is not an entirely desirable alternative, however,since such solvents do not polymerize or copolymerize but merely areentrapped in the polymerized material, thus not contributing to itsdesirable properties.

In preferred embodiments the monomers of this invention are employed incomonomer compositions which compositions which comprise admixtures ofthe bis(2-cyanoacrylates) and at least one polymerizable monofunctionalester of 2-cyanoacrylic acid. Initiation and propagation ofpolymerizaion of such compositions is accomplished by means of ananionic catalyst as hereinafter described or, alternatively, by thermalor other means recognized as being suitable for initiating thepolymerization of monomers having the cyanoacrylate function present intheir structure.

Desirable esters of 2-cyanoacrylic acid include alkyl esters of2-cyanoacrylic acid, wherein the alcoholic moiety of the ester is eitheran alkyl group of from 1-16 carbon atoms, a cyclohexyl group, or aphenyl group. The monofunctional 2-cyanoacrylate, being a liquid at roomtemperature, functions as a reactive comonomer and solvent for thedifunctional bis(2-cyanoacrylates). The bis (2-cyanoacrylate) monomer isan effective crosslinking agent when included in amounts as small as 1%by weight based on the total weight of the monomers present. Generally,improvements in polymer properties such as breaking strength areobserved when higher concentrations of crosslinking difunctionalmonomers are included, up to and including the maximum amount soluble inthe monofunctional 2-cyanoacrylate ester.

In Table I, illustrative maximum solubilities of various difunctionalmonomers of this invention in isobutyl 2-cyanoacrylate are noted. Onceone has determined which difunctional monomer and which monofunctionalmonomer he desires to include in blend of these monomers, it is a simpletask to determine the maximum solubility of the difunctional monomer inthat specific ester of 2-cyanoacrylic acid. Less than the maximum amountsoluble can, of course, be employed, while still obtaining excellentcrosslinking with the ester of 2-cyanoacrylic acid and giving a polymerhaving improved adhesive properties.

                                      TABLE I                                     __________________________________________________________________________    Maximum Solubility of Bis (2-Cyanoacrylate) Monomers in                       Isobutyl 2-Cyanoacrylate at Room Temperature.                                 __________________________________________________________________________                            % By Weight (approx.)                                 __________________________________________________________________________    Ethylene glycol bis (2-cyanoacrylate)                                                                 5                                                     1,3-Propanediol bis (2-cyanoacrylate)                                                                 9                                                     1,4-Butanediol bis (2-cyanoacrylate)                                                                  15                                                    trans-2-Butene-1,4-diol bis (2-cyanoacrylate)                                                         7                                                     1,6-Hexanediol bis (2-cyanoacrylate)                                                                  34                                                    2,5-Hexanediol bis (2-cyanoacrylate)                                                                  25                                                    1,8-Octanediol bis (2-cyanoacrylate)                                                                  17                                                    1,9-Nonanediol bis (2-cyanoacrylate)                                                                  32                                                    1,10-Decanediol bis (2-cyanoacrylate)                                                                 7                                                     1,12-Dodecanediol bis (2-cyanoacrylate)                                                               6                                                     1,3-bis (Hydroxymethyl) tetramethyl-                                          disiloxane bis (2-cyanoacrylate)                                                                      ∞                                               __________________________________________________________________________

In order to initiate the polymerization reaction of either the monomersor the comonomer blends of this invention, it is suitable to use a basiccatalyst such as a metal hydroxide, a basic salt, ammonia, or organicamines. Other weak nucleophiles such as water and alcohol also caninitiate reaction. Polymerization by free radical and thermal means isalso possible, but anionic initiation is preferred and favored becauseof the presence of strong electron withdrawing groups in thecyanoacrylate monomer structure.

In general, those catalysts or initiators that are suitable for thepolymerization of esters of 2-cyanoacrylic acid, whether chemical innature or in the form of radiant energy, are suitable for initiating andpropagating polymerization of the monomers of this invention whether ashomopolymers, or copolymers from monomer blends thereof, or incombination with esters of 2-cyanoacrylic acid.

Preferred catalysts are the organic amines, especially tertiary amines;specific examples of which include N,N-dimethylaniline,N,N-diethylaniline, N-methylbenzylamine, triethanolamine, triethlamine,diethanolamine, diethylamine, 2-picoline, 4-picoline, tributylamine,4-ethylpyridine, pyridine, N,N-diethylethylenediamine,N,N-dimethyl-p-toluidine, N,N-diethyl-1-napthylamine, andhexamethylenediamine. Of these, N,N-dimethyl-p-toluidine is preferred.

Only a trace amount, e.g., 0.005% by weight of catalyst is necessary toinitiate polymerization. Yet, to evenly distribute such a trace amountthroughout a monomer, or comonomer blend, is rather difficult.Therefore, a convenient and preferred technique for catalysis of filledcyanoacrylate compositions is to incorporate the trace amounts of aminecatalyst required on the filler particles. On stirring a monomer/fillerblend, the catalyst diffuses from the filler particles into thecomposite mixture. The catalyzed composition proceeds through an initialinduction period, during which the mixture maintains a relativelyconstant working viscosity. This is followed by a gellation stage whichin turn is rapidly followed by an almost instantaneous transition (in5-15 seconds) to a hard composite mass.

Unfilled bis (2-cyanoacrylate) monomers, or their comonomer blends withother cyanoacrylates, are catalyzed by contacting the neat monomer witha very small amount of alumina which has been pretreated with a highconcentration of the amine catalyst, generally 4% by weight based on thealumina. The amine catalyst diffuses from the alumina particles into themonomer phase. The catalyzed monomer phase is separated from the verysmall amount of alumina-catalyst particles by allowing them to settleout to the bottom of the mixing vessel, or even removed if desired,prior to gellation. The time required for the catalyzed monomer to reachthe gellation and polymerization stage can be varied by modifying themonomer/catalyst carrier contact time, weight ratio of monomer tocatalyst carrier, catalyst concentration on the alumina particles, andsulfur dioxide inhibitor level in the monomer.

In preparing compositions that are to be worked or shaped afterinitiating catalysis, such as those employed in dental applications, theperiod from the onset of mixing to the beginning of the gellation stage(gel time) is the time period during which the composition can beworked. After the gellation stage has begun, through to a period oftransition to a hard set material, the polymerizing material ought notbe disturbed. For pit and fissure sealant formulations gel times of 1-2minutes and transition times of 5-15 seconds are desirable. Specific geland transition periods can be obtained by decreasing and increasing theamounts of catalyst and the amount of monomer inhibitor, such as sulfurdioxide, or the balance between catalyst and inhibitor. The use ofsulfur dioxide inhibitors in 2-cyanoacrylate systems is well known andneed not be discussed here in detail.

The comonomer blends of this invention employing a monofunctionalmonomer consisting of an ester of 2-cyanoacrylic acid can be utilizedeither in filled or unfilled systems. When a filler is employed, it canbe any material resistant to the abrasion, erosion, or corrosive attackby substances that are likely to contact the polymerized filledmaterial. Such fillers can be powdered metal or metal oxides, silica orsilicacious materials, carbides, and the like. For dental applicationsthe preferred fillers are quartz and alumina. Other fillers such asglass and polyethylene may be used. For dental and other applicationsthe particle size should substantially be in the range of from 1 to 100microns. Larger particles are not deleterious, but do not provide asmooth textured material. Similarly, smaller particles are not desirablesince they are too small to serve as a good aggregate. The filler ifused should be employed in amounts sufficiently large to be of value,e.g., at least 10% by weight, and should not be used in so large aquantity, e.g., more than 85% by weight, that all the filler particlesare not wetted by the monomer or monomer blend. Generally, a desirablequantity of filler will be in the range of from 50% to 80% by weight.These percentages of filler are based on the total weight of monomersand filler present in the composition.

In Table II there is summarized the lap shear adhesion and the breakingstrength properties of various polymeric compositions prepared from bothfiller and unfilled blends of difunctional monomers and isobutyl2-cyanoacrylate. Each blend was catalyzed with N,N-dimethyl-p-toluidineby the appropriate technique as heretofore discussed.

The compositions set forth in Table II can be suitably employed as pitand fissure sealants. The patient's mouth is first rinsed with an oralantiseptic and then with water. The teeth are isolated with cottonrolls, thoroughly dried with an air syringe, and etched forapproximately one minute with phosphoric acid. The patient then riseshis mouth thoroughly with water to remove the acid from the toothsurfaces. The teeth are again isolated with cotton rolls and againthoroughly dried. The pit and fissure sealant prepared according to theforegoing description is then applied by conventional techniques.

Breaking strengths are measured by compression testing on an Instrontester at a strain rate of 0.02 inches per minute. Cylindrical testspecimens, measuring 0.15 inch in diameter and 0.30 inch length, areprepared by pouring catalyzed monomer compositions into Teflon molds,allowing the mass to polymerize, extruding the specimens from the molds,polishing the ends flat and smooth, and conditioning the specimens inwater at 100° F for 24 hours prior to compression testing. Thestress/strain curve on compression consists of a brittle component and aviscoelastic type component which is evident beyond the yield point.Breaking strengths reported are calculated from the compressive forcevalves where the specimens undergo a physical breakdown, as determinedinstrumentally, and are invariably of greater magnitude than the yieldstrengths at the proportional limit.

Shear adhesion measurements were made on carefully cleaned steel plates(0.5 inch × 2 inches × 0.1 inch) cemented together to give a 0.5 × 0.5inch lap joint. A 37.5 gram weight was placed on top of the joinedsurfaces until a firm adhesive bond was established. The specimens wereconditioned at room temperature for 24 hrs. and the shear adhesive forcemeasured on an Instron tester at a strain rate of 0.5 inch per minute.

                                      TABLE II                                    __________________________________________________________________________    STRENGTH PROPERTIES OF FILLED AND UNFILLED CYANOACRYLTE POLYMER               COMPOSITIONS                                                                  __________________________________________________________________________                % Monomer Content Based On                                                    Total Weight Monomers                                                         Present In Composition                                                                        Filler Content Based On                           Difunctional Bis                                                                          Percent                                                                              Percent  Weight Total Composition                                                                       Lap Shear                                                                           Breaking Strength          (2-Cyanoacrylate) of                                                                      Difunctional                                                                         Isobutyl-2-                                                                            Alumina Filler                                                                         Quartz Filler                                                                         Adhesion                                                                            PSI                        the Diol-   Monomer                                                                              (Cyanoacrylate)                                                                        % By Weight                                                                            % By Weight                                                                           PSI   Range  Average             __________________________________________________________________________      --        0      100      72-75    0       1370  5470-8220                                                                            6850                  --        0      100      0        80      --    6470-6960                                                                            6760                            0      100      0        0        660  5220-6840                                                                            6130                Ethylene glycol                                                                           4      96       75       0       1410  6520-7460                                                                            6860                Ethylene glycol                                                                           20     80       72       0       --    8000-8970                                                                            8380                Ethylene glycol                                                                           4      96       0        80      --    6880-7860                                                                            7410                Ethylene glycol                                                                           4      96       0        0       1150  4030-22920                                                                           7070                1,3-Propanediol                                                                           9      91       73.5     0       --    5540-7650                                                                            6560                1,3-Propanediol                                                                           9      91       0        0       1260  5230-7490                                                                            5840                1,4-Butanediol                                                                            15     85       72       0       --    8410-9350                                                                            8710                1,4-Butanediol                                                                            15     85       0        0       1160  5420-10600                                                                           7880                Trans-2-butene-1,4-diol                                                                   7      93       72       0       --    7840-8520                                                                            8130                Trans-2-butene-1,4-diol                                                                   7      93       0        0       1420  5870-7710                                                                            6460                2,5-Hexanediol                                                                            25.6   74.4     73.5     0       --    5790-7560                                                                            6710                2,5-Hexanediol                                                                            24     76       0        0       --    6540-10070                                                                           7720                1,6-Hexanediol                                                                            34     66       73.5     0       --    7050-8820                                                                            7950                1,6-Hexanediol                                                                            34     66       0        80      --    8560-9570                                                                            9120                1,6-Hexanediol                                                                            7      93       0        0       --    7550-37010                                                                           16280               1,6-Hexanediol                                                                            30     70       0        0        450  9810-12810                                                                           11460               1,6-Hexanediol                                                                            34     66       0        0       --    6630-16790                                                                           10540               1,8-Octanediol                                                                            17.6   82.4     73.5     0       --    6320-7070                                                                            6640                1,8-Octanediol                                                                            17     83       0        0       --    5750-10200                                                                           8270                1,9-Nonanediol                                                                            10     90       75       0       1700  7660-8460                                                                            8070                1,9-Nonanediol                                                                            33     67       73.5     0       --    4480-7610                                                                            5880                1,9-Nonanediol                                                                            8      92       0        0       1320  12340-21180                                                                          17760               1,9-Nonanediol                                                                            30     70       0        0        620  13300-22880                                                                          16740               1,10-Decanediol                                                                           7.5    92.5     73.5     0       --    5560-7330                                                                            6170                1,10-Decanediol                                                                           7.5    92.5     0        80      --    6880-7370                                                                            7070                1,10-Decanediol                                                                           7.5    92.5     0        0        880  5170-17460                                                                           10880               1,12-Dodecanediol                                                                         6.7    93.3     73.5     0       --    5100-6390                                                                            5700                1,12-Dodecanediol                                                                         6.5    93.5     0        0       1990  5100-7650                                                                            6850                1,3-bis (hydroxymethyl)                                                       tetramethyldisiloxane                                                                     50     50       73.4     0       --    2980-5820                                                                            4170                1,3-bis (hydroxymethyl)                                                       tetramethyldisiloxane                                                                     100    0        0        75      --    3400-5820                                                                            4610                1,3-bis (hydroxymethyl)                                                       tetramethyldisiloxane                                                                     100    0        0        0        300  11790-21390                                                                          >15870              __________________________________________________________________________

From Table III it can be observed that upon aging in water at anelevated temperature (100° F), the breaking strength of polymerizedcomonomer blends improves. Incidentally, these are the conditions oftemperature that prevail in warm blooded animals' mouths, making thesecompositions especially suitable for dental applications.

                                      TABLE III                                   __________________________________________________________________________    Effect of Aging Time at 100° F in Water on Breaking                    __________________________________________________________________________    Strength                                                                      Monomer:                                                                            Isobutyl-2-cyanoacrylate/Ethylene Glycol Bis (2-                              Cyanoacrylate) (EGBCA)                                                  Filler:                                                                             Alumina, 72% w                                                          Isobutyl-2-Cyanoacrylate/                                                                     Breaking Strength, psig (avg.)                                EGBCA (w/w) Monomer Mix                                                                       100° F/24 hrs.                                                                   100° F/7 days                                __________________________________________________________________________    100% IBC (Control)                                                                            6350      6870                                                99/1            6520      8140                                                98/2            6380      7790                                                96/4            7360      8700                                                94/6            7600      9300                                                90/10           8160      --                                                  80/20           8380      --                                                  __________________________________________________________________________

Furthermore, it can be seen from Table IV that this increase in breakingstrength is not limited to polymerized comonomer blends of the monomersof this invention and isobutyl-2-cyanoacrylate, but extends to esters of2-cyanoacrylic acid generally.

                                      TABLE IV                                    __________________________________________________________________________    Effect of the Alkyl Group in Alkyl 2-Cyanoacrylate Monomers                   on Breaking Strengths of Crosslinked Alumina Filled                           Composites                                                                    __________________________________________________________________________    Crosslinking monomer:                                                                     Ethylene Glycol Bis (2-Cyanoacrylate)                                         (EGBCA)                                                           Filler:     72% w Alumina                                                                    Breaking Strengths, psi                                        __________________________________________________________________________    Alkyl Group of Alkyl Cyano-                                                                            Cyanoacrylate +                                      2-Cyanoacrylate Monomer                                                                      acrylate alone                                                                          3.6 mole % EGBCA                                     __________________________________________________________________________    Ethyl          7290      6060                                                 Isobutyl       5470      7180                                                 n-Amyl         2160      3070                                                 i-Amyl         4590      5060                                                 n-Hexyl         980      1450                                                 n-Heptyl        390       670                                                 __________________________________________________________________________

EXAMPLE XXVI

Improvement in resistance to moisture of cyanoacrylate bonds through theinclusion of small amounts of biscyanoacrylate monomer in the monomermix used is illustrated.

Steel plates, 1/2 inch × 2 inch × 0.1 inch were freed of rust andcleaned by successive immersion in dilute hydrochloric acid, water,dilute ammonium hydroxide, water, and acetone.

Bonding was effected by addition of a small drop of cyanoacrylatemonomer on the end of one plate, followed by careful placement of theother plate to give a 1/2 inch × 1/2 inch lap joint. A 37.5 gram weightwas placed on the lap joint until adhesive bonding took place. A set of10 specimens was prepared for shear adhesion testing under theconditions shown in the accompanying Table. The abbreviation 100° F/H₂O/1 day indicates, for instance, that the specimen was kept immersed inwater at 100° F. for 1 day prior to the shear test.

The IBC (isobutyl 2-cyanoacrylate) monomer formulations were allcatalyzed with a trace amount of N,N-dimethyl-p-toluidine catalyst inorder to effect an adhesive bond within two minutes. The MCA (methylcyanoacrylate), a commercial adhesive (Loctite* Quick-Set Adhesive 404;Loctite Corp.), and its blend with the crosslinking monomer,1,8-octanediol bis(2-cyanoacrylate), formed an almost instantaneous bondand did not require addition of a catalyst.

All crosslinkable cyanoacrylate formulations were based on a 90% alkyl2-cyanoacrylate and a 10% w 1,8-octanediol bis(2-cyanoacrylate)(1,8-ODBCA) blend.

Shear adhesion testing was done on an Instron tester at a pull-rate of0.5 inches/minute. The values shown in the Table are averages of 10specimen measurements.

Based on the tabulated data, the following conclusions can be reached:

While MCA gave higher initial bond strengths than the IBC, the shearadhesive bond strength of the former deteriorated to about 30% of theinitial bond strength after 7 days in water at 100° F. The IBC and thecrosslinked IBC bonded specimens were not affected under the sameconditions. The crosslinked IBC bond strength was at least 20% greaterthan that obtained with IBC alone. Incorporation of the crosslinkingmonomer into MCA did not appear to improve the initial bond strength butgave an adhesive bond which was much more resistant to degradation inwater, comparing for example the 7 day drop from 2612 to 780 psi for MCAvs the 2000 to 1156 psi for the cross-linked MCA. After 7 days in water,the crosslinked MCA bond strength (1156 psi) was about 48% greater thanthat of the non-crosslinked MCA (780 psi).

                                      TABLE                                       __________________________________________________________________________    SHEAR ADHESIVE BOND STRENGTHS OF                                              CROSSLINKED VS NON-CROSSLINKED IBC AND MCA                                    __________________________________________________________________________                Shear Adhesive Bond Strength, in psi                                              90/10        90/10                                            Conditioned at                                                                            IBC IBC/1,8-ODBCA                                                                          MCA MCA/1,8-ODBCA                                    __________________________________________________________________________    100° F/air/1 day                                                                   508 612      2612                                                                              2000                                             100° F/H.sub.2 O/1 day                                                             512 812      1660                                                                              1476                                             100° F/H.sub.2 O/7 days                                                            524 628       780                                                                              1156                                             __________________________________________________________________________

From the foregoing description, it is apparent that the objects of thisinvention have been achieved in a new and novel manner. While onlyspecific embodiments have been illustrated, it should be apparent fromthe foregoing description to those skilled in the art that otheralternatives can be practiced within the spirit and the scope of thepresent invention.

What is claimed is:
 1. A monomer composition of the formula ##STR20##